Switching apparatus for telephone-exchanges.



-No. 753,927. I PATENI'ED MAR. 8,1904.

' E. H. SMYTHE.

SWITCHING APPARATUS FOR TELEPHGNB EXCHANGES.

' APPLIOATION FILED MAR, 10, 1902.

1N0 MODEL.

y I jjdmffif iizji za; MA JIO'VYM. yffww UNTTED STATES Patented March 8, 1904.

P TENT OFFICE.

EDWIN H. SMYTHE, OF FREEPORT, ILLINOIS, ASSIGNOR TO IVESTERN ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

SWITCHING APPARATUS FOR TELEPHONE-EXCHANGES.

SPECIFICATION forming part of Letters Patent N0. 753,927, dated March 8, 1904;,

Application filed March 10, 1902. Serial No. 97,388. (No model.)

To all whom, it may concern.- Be it known that I, EDWIN H. SMYTHE, a citizen of the United States, residing at Freeport, in the county of Stephenson and State of Illinois,have invented a certain new and useful Improvement in Switching Apparatus for Telephone-Exchanges, of which the following is a full, clear, concise, and exact description.

This invention applies to telephone exchange systems in which the current for operf ating the substation-transmitters is supplied 3 I senting'a telephone-line entering the answering-switchboard at a centraloflice and there from a central source of current applied to the lines through the agency of the link conductors employed in uniting them for conversation. It is usual in such systems to provide secondary signals controlled by electromagnets in the path of the supply-currents, the circuit of such currents being controlled by the telephon e-switches at the substations. Automatic supervision of the united lines is thus obtained as an incident to the supply of current over them. The complete organization of the circuits and mechanism has come to be known as the central-battery automatic-signal switchboard. For various reasons, one of which is the necessity for making connection with grounded lines, it is usual to ground one pole of the source of current connected with the link conductors for uniting lines; but in any case in a large exchange the source of current is practically grouhded through the leakage and capacity of the united lines connected therewith. When link conductors thus connected with the common source of current are employed in uniting subscribers lines with trunk-lines slightly out of balance and sub: jected to inductive disturbances from neighboring power or lighting circuits, the metallic trunk-line circuits are made 'noisy bythe induced disturbances and in many cases are rendered useless for the proper transmission of telephonic currents; My invention is intended for use in such systems and aims to free the link conductors from the detrimental ground connections when they are used in uniting subscribers lines with trunk-lines, the function of severing the normal connections of the link conductors and arranging them in circuits free from grounds being delegated to an appliance by which the operation is automatically determined in making connection with the trunk-line. I

The invention also embraces a system of signals and operating-circuits therefor bei tween the different terminals of the trunk-line, adapted to the conditions imposed by the first: mentioned feature.

The invention is illustrated in the accom: panying drawing, which is a diagram repreconnected with a trunk-line which extends to a distant trunking-board where other lines are centered.

The apparatus at the telephone-substation,

' which is designated by the letter A, is such as has become well known in the art of telephony under the name of central-battery station set. i are permanently united through a bridge, in-

The conductors of the line-circuit cluding the call-bell a of the station, together with a condenser a which maintains the separation of the two limbs with respect to continuous currents, and the telephone apparatus proper is included in a normally open bridge controlled by the telephone-switch. The line conductors 1 and 2 lead from the station apparatus to a spring-jack 6 in a central-office an swering-switchboard A and are connected with the two poles of a centralsource of current. A relay controlling a secondary line-signal 0 is interposed .in the extensions from the springjack to the battery. The continuity of these normal extensions is controlled by the switchcontacts of a cutoff relay (Z, which is included in a part of a local conductor which is designed to be united during connection with the line with other local conductors in a local circuit including current for exciting the relay, so that the line is freed from its normal connections with the line-signal apparatus during to unite them, have each three contact-pieces to register with the three metallic contact por tions of the jack. The so-called line-contacts g and g of the plugs are, in effect, united by conductors 3 4 and 5 6, respectively, conductor 3 leading from contact g of plug f through a Winding h of a repeating-coil it to one pole of a battery 2', while conductor 4: leads from contact g of plug f through a second winding k of the repeating-coil it to the same pole of battery z'. This pole of the battery is grounded. The connection of conductor i with the battery is controlled, however, by the switch-contacts of a relay or electromagnetic switch is, which will presently be described. Likewise contact g of plug f forms the terminal of conductor 5, leading from the opposite pole of battery 2', traversing another winding if of repeating-coil It, while contact 9 of plug f forms the terminal of conductor 6, leading to the same pole of battery Z through winding it, the latter circuit being also controlled by the relay la. The magnets of relaysZ and Z are interposed in conductors 5 and 6, respectively, and control supervisory signals m and m. These signals on and m are small incandescent lamps, located in two conductors 7 and 8, respectively, leading from the free pole of battery Z to contacts g of their corresponding plugs. The relay Z controls a shunt 9 about the lamp m, and the relay Z controls a conductor 10, which is associated with the lamp m, being at times in shunt of the lamp and at other times in series therewith, according to the condition of the electromagnetic switch k. The plug-circuit would in practice have the usual listening and calling keys, which are, however, omitted for the sake of clearness in the drawing.

The magnet-winding of the electromagnetic switch is interposed in conductor 8 between the lamp m and the plug-contact The inner terminals of windings b and h are connected with switch-levers 7c and k of this relay, whose normal resting contacts are electrically united by a conductorll, but whose inner contacts, against which the levers are brought when the magnet is excited, are connected with the two poles of battery 2 The relay has also a third switch-lever 70 which controls the circuit of the conductor 10. The resting contact of the lever is connected through a resistance-coil to earth, and the alternate contact thereof is connected to the free pole of battery z. The conductor 10 may include a resistance, as shown. When the switch it is in its normal position, therefore, the contacts of relay Z are in series with the lamp m, controlling the circuit 8 10; but when the armature 7: of the switch is is drawn up the conductor 10 is placed in shunt of thelamp this shunt being controlled by the relay Z.

Between the ofiices A and B extends atrunkline 13 14, terminating in a jack 6 in the switchboard at ofi'ice A. A repeating-coil 0 is interposed in the trunk-line at the board B, conductively dividing the main section of the trunk line from the extensions 15 and 16 thereof, which lead to the terminal plug f. The circuit is, however, inductively continuous from one end to the other.

In order that the two conductors 13 and 14: of the trunk-line may be used for the purpose of transmitting signals between the offices A and B while the trunk-line is not in use for conversation, it is convenient to employ the said conductors in connection with the ground ed battery 9 until the moment of conversa tion and also after the conversation has ended; but in order that the lines may be tree from ground connections during the transmission of telephonic currents I have provided a relay or electromagnetic switch 19, of which the function is to sever the normal ground connections and complete direct circuits between the wires during conversation, the relay being itself controlled through the agency of the telephone-switch at the called station. The relay 19 has two switch-levers p and 19 each with normal and alternate contact anvils. The normal resting contact of lever 13 is connected to ground. Its inner contact and the outer contact of lever p are connected by a wire 17 to the inner extremity of winding 0 of the repeating-coil, which leads to the terminal of conductor 14: of the trunk-line. Lever 19 is connected with the inner end of winding 0, which forms the terminal of conductor 13 of the trunk-line. The switchlever 19 forms the terminal of a wire 18, leading to the free pole of a grounded battery g, which may be the central source of current-supply for the exchange-office B, the magnet-winding of a relay 0" being interposed in this conductor. The inner or alternate contact of lever 19 forms the terminal of a wire 19, leading to the grounded pole of battery q through a considerable resistance.

The two conductors l5 and 16 lead from the poles of battery q through the induction-coil windings 0 0 respectively, to the. line contact-pieces g and g of terminal plug f The third contact-piece of the plug f forms the terminal of a conductor 22, which includes the magnetwinding of a relay 8, together with a supervisory or ringing signal 41, which is associated with plug f in a switchboard and denotes the condition of the line called for with respect to the use of the telephone, the conductor leading finally to the free pole of battery 9.

Switchcontactsnamely, s s of the relay scontrol the continuity of a local circuit 20 of battery q, including the clearing-out si nal-lamp u and a resistance-coil t. The illumination of this clearing-out signal-lamp is determined by a shunt 21 thereof, controlled by the switch-contacts of relay 0".

A supervisory relay w is placed in the path of current in conductor 16, its switch-contacts controlling a local circuit of battery q, formed in part of wires 23 and 24, of which the latter includes the magnet-winding of relay p. The former is connectedwith wire 22 on either side of the lamp 11, forming a shunt about said lamp. This shunt-wire 23 includes the winding and switch-contacts of a relay :0. The wire 24 is connected to the wire 23 between the magnet-winding of the relay and its switch-contact, a local circuit from battery (1, including relays a: and 19, being thus formed by wires 22, 23, and 24, this local circuit being controlled at the switch-contacts of the supervisory relay w. The relay 00 once excited closes the shunt 23, which includes its own winding, so that the shunt about the lamp is held closed subject to the withdrawal of the plug f from the spring-jack into which it may have been inserted.

It is understood that the usual order-wire may be provided between the switchboards A and B, whereby the operators may converse directly with each other.

The taking of the telephone at station A for use closes the local circuit and displays the secondary line-signal in the switchboard at office A, which calls the attention of the answering or supervising operator at that oifice, who inserts her answering-plug f.

into the spring-jack 6 of the calling-line. The plug being in the socket closes a local circuit made up of conductor 7, leading from battery i to the contact-piece g of the plug and the conductor leading to earth from the contactring of the spring-jack through the magnet of the cut-off relay. The latter appliance being excited by current in this circuit severs thenormal connections of the line and extinguishes the line-lamp. At the same moment current from battery '5 flows throughwindings lb and if of the repeating-coil by way of conductors 3 and 5 of the plug-circuit to the subscribersline, traversing the relay Z, which closes its shunt 9, and so extinguishes the signal-lamp m. The operator then inquires by telephone in the 'usual manner the number of the subscriber wanted. Now if this order were for a party whose line terminated within the exchange A the operator would test a spring-jack ofthe line called 'for by touching the tip of the calling-plug to the ring of the jack and listening in her telephone in the usual way. The operators telephone isnot shown, but may be inductively connected with the tip of the calling-plug in a well-known manner through the contacts of a listening-key. Then if the called line were free she would insert plug f fully into the springjack thereof, by which a local circuit would be formed from the contact-piece g of the plug similar to that traced for plug f, the circuit being from battery z through wire 8, including lamp m and relay k, to the plug, thence to the contact-ring of the spring-jack and to earth through the cut-oil relay.. The

circuit from the wire 11 and connect it with the free pole of battery 4; the lever 10 would disconnect the wire 10 from its normal direct earth connection and would connect it with the free terminal of grounded battery t' or an equivalent source of current. The portion of the-plug-circuit leading to plug f" is thus re arranged by the electromagnetic switch to be like the portion of the circuit leading from the battery to the plug f-that is, to supply current from battery 2' to the line called for.

The current thus flowing to the line will traverse the magnet-winding of relay Z, and thus effect the control of supervisory signal m, the wire 10 being, in effect, a shunt about thelamp m, whose continuity is determined by the switch-contacts of relay Z. Thus the portion of the plug-circuit destined to be associated with the called line, while normally not adapt- 5 ed for use in such connection, is automatically shifted into connection with battery in the act of making connection with the subscribers line.

Assume now that the call of the calling party a be for a line entering the central station B, so that the connection shall involve the use of the trunk-line 13 14. The operator addresses the incoming trunk operator at office B over an order-wire (not shown) and instructs her to make the connection with the line to the desired station, receiving in response instruc: tion as to which trunk-line to use. The subscribers operator then inserts plugf'into the spring-jack b of the designated trunk-line, and the incoming trunk operator at ofiice B, taking the terminal-plug f of the designated trunk-line, tests the spring-jack of the line called for in the usual way and if she finds it free inserts plug f into the spring-jack and sends a call-signal to the substation of the line. When the plug f is in the jack, a local circuit is completed from battery 9' through wire 22, including lamp '2) and windingof relay s,s'leeve of plug f contact-ring of spring-jack b and the cut-off relay of the called line. The excitement of relay 8 by current traversing this circuit closes together contact-pieces 8 stand thereby completes the circuit of battery q through conductor 20, including the clearingout signal a, which may become lighted, subject I to the control, however, of the plug f and spring-jack Z) at the outgoing terminal of the trunk-line. The insertion of plugf into thespring-jack b connects conductors 4 and 6 of the plug-circuit with conductors 13 and 14 of the trunk-line, and thus, in effect, extends the circuit from the calling-station to the terminal plug f and so to the line of the station called for. The ring or third contact of spring-jack b has no electrical connection, so that the local circuit terminating in plug f remains open and the relay is inert, Conductors 4 and 6 are thus directly united through a path including windings 7L and h of the repeating coil and wire 11, while wire 10 is connected directly to earth through a resistance-coil, thus furnishing a path for current from battery 2' through conductors 8 and 10, including the signal lamp m, this circuit being controlled, as before, by the switch-contacts of supervisory relay Z. The conductors of the trunkline at the oflice Awhich are involved in telephonic transmission are thus left free from ground connections. The lamp m is lighted, its illumination being determined by the connection of battery q with conductors 13 and 14 of the trunk-line at ofiice B. When the party at the called station answers by removing the telephone from its switch, a circuit of battery q is closed by the switch, and the flow of current excites the supervisory relay w and brings about a new disposition of the circuits, as follows: The closure of the switch-contacts of relay to forms a circuit from battery q by way of conductors 22, 23, and 24, which includes the magnets of relays p and 00, both of which draw up their armatures. Relay it closes the shunt about the signal-lamp Q), which until then was lighted. Relay 1) severs the connection of conductors 13 and 14 with battery q and connects these conductors directly together through wire 17, at the same time breaking the connection between wire 18 and wire 14 and uniting wires 18 and 19, forming a local circuit including the magnet of relay '1'. This relay stays excited and maintains the shunt 21 closed about the clearing-out lamp a. The response of the called party thus brings about the extinction of signal-lamp 'u and indicates to the incoming trunk operator the response to the call, frees the trunk-line at the incoming terminal from all normal ground connections, and by depriving relay Z of current extinguishes the lighted supervisory-signal lamp m at oflice A, indicating to the subscribers operator the answer to the call. Supervision of the completed connection may be assigned to the subscribers operator at office A;

It will be apparent that the replacement of the telephone on its switch at station A will cause the lighting of supervisory signal m, while the replacement of the telephone on its switch at the called station will bring about the illumination of signal m by depriving the relay 1; of current, and thus reestablishing the conditions before described. The simultaneous lighting of both signals may be accepted as meaning a signal for disconnection and will be followed by the removal of plugs f and f from the spring-jacks of the subscribers line and the trunk-line, respectively. The withdrawal of plug f from jack 6 leaves the relay r inert, so that the shunt 21 of clearing-out lamp u is broken. The consequent lighting of this signal-lamp calls for disconnection of the trunk-line from the line of the called party.

I claim as new, and desire to secure by Letters Patent, the following:

1. The combination with telephone-lines of two different types entering an exchange-office and provided with spring-jack terminals thereat, of apair of plugs and their plug-circuit for uniting any two of said lines, an induction device dividing the plugcircuit, a battery in a bridge of the conductors leading to the answering-plug, an electromagnetic switch controlling the connection of said battery with the conductors leading to the calling-plug, and a local circuit for said electromagnetic switch, operatively established in registering contacts of the calling-plug and the spring-jack of any of the lines of one of said types; whereby the battery is brought into the circuit by connection with a line of one type, but is not brought into the circuit by connection with a line of the other type.

2. The combination with subscribers telephone-lines and a telephone trunk-line terminating in spring-jacks at an exchange-switchboard, of a pair of plugs and their plug-circuit, a repeating-coil dividing the plug-circuit, a battery connected in a bridge of the plugcircuit together with that winding of the repeating-coil which is connected to the answering-plug of the pair, one pole of said battery being grounded, an electromagnetic switch adapted to connect the battery in circuit with the calling-plug, and a circuit for the said electromagnetic switch established in registering contacts of the callingplug and the spring-jack of any subscribers line, said circuit being left incomplete by the insertion of the calling-plug in the spring-jack of the trunkline whereby the plug-circuit may beconnected with the trunk-line without grounding the trunk-line.

8. The combination with two subscribers lines and a trunk-line for uniting them, of a pair of plugs and their plug-circuit connecting one of the subscribers lines with one end of the trunk-line, and means for connecting the other end of the trunk-line with the other subscribers line, a grounded battery in the plug-circuit, a second grounded battery connected with the trunk-line at the end distant from the plug-circuit, signals for the system supplied with current from said batteries, two induction devices conductively separating the main section of the trunk-line from the two subscribers lines, and automatic switches adapted to cut off the said batteries from the conductive connection with the main section of the trunk-line, whereby inductive or electrostatic disturbances or unbalancing of the circuit during telephonic conversation overthe trunk-line is avoided.

e. The combination with subscribers telephone-lines and a trunk-line, terminating in spring-jacks at an exchange-switchboard, of a pair of plugs and their plug-circuit, an induction device dividing the plug-circuit, a grounded source of current connected with one end of the plug circuit, an electromagnetic switch controlling the connection of said source of current with the other end of the plug-circuit, a conductor adapted to form a portion of a local circuit for said electromagnetic switch, terminating in a contact-piece of the plug-terminal of the last-mentioned end of the plug-circuit, and conductors connected to contact-pieces of the spring-jacks of the several subscribers lines, adapted to complete the local circuit of said electromagnetic switch when the plug is inserted in such spring-jacks, whereby the said switch is caused to connect the battery with a subscribers line when the plug is inserted in the spring-jack of thatline, the battery being disconnected when the plug is inserted in the spring-jack of the trunk-line.

5. The combination with a trunk-line, a called-subscribers line connected to the trunkline at the receiving-terminal thereof, a calling-subscribers line, and a pair of plugs and their plug-circuit uniting the calling-subscribers line with the other terminal of the trunk-line, of a battery conductively connected with the plug-circuit, a battery conductively connectedwith the trunk-line at the receiving-terminal thereof, signals supplied with current from said batteries, an induction device dividing the plug-cir'cuit, another induction device at the receiving-terminal of the trunk-line conductively dividing the trunkline from the called-subscribers line, and switches at each terminal of the trunk-line adapted to cut ofi" the batteries from conductive connection with the trunk-line, whereby inductive and electrostatic disturbances on the trunk-line during its use for speech trans-' a source of current in the section of the trunkline which terminates in the trunk-plug, a telephone-line connected with the trunk-line at the trunking-board, said relay being controlled through the agency of the telephoneswitch at the substation of the telephone-line, and a local circuit for the electromagnetic switch, controlled by said supervisory relay, substantially as described.

7. The combination with twotelephone-lines and a trunk-line uniting them, of induction devices conductively severing the telephonelines from the trunk-line, a signal device Z at one end of the trunk-line responsive to the flow of battery-current therein, a grounded battery connected with the trunk-line at the other end thereof for operating said signal device, an electromagnetic switch 12 for disconnecting the battery from the trunk-line, the telephone-circuit being completed independent of said battery,-a switch at the substation of one of the telephone-lines, and means controlled by said switch for operating the aforesaid electromagnetic switch 10, whereby the trunk-line is freed from connection with the grounded battery during the use of said trunkline for telephonic purposes, and the battery is connected with the line at other times for signaling purposes.

8. The combination with two telephone-lines of different types, each line having a springjack terminal at an exchange-switchboard, of a plug and plug-circuit for making connection with either of said lines by the insertion of the plug into the corresponding spring-jack, a source of current, a supervisory signal in a local circuit with said source of current, a re lay in the plug-circuit controlling said supervisory signal, an electromagnetic switch controlling the operative relation of the relay to the supervisory signal, said electromagnetic switch being adapted alternatively to bring the switch-contacts of the relay into series or shunt relation with said signal, and a circuit for said electromagnetic switch operatively completed in registering contacts of the plug and one of said spring-jacks but not the other, whereby the operative relation between the supervisory relay and its controlled signal is dependent upon the type of line with which the plug-circuit may be connected.

In witness whereof I hereunto subscribe my name this 7th day of March, A. D. 1902.

EDWIN H. SMYTHE.

Witnesses:

DE WITT C. TANNER, GEORGE PRESTON BARTON. 

